Rare-earth element mineralisation within the Mt. Weld carbonatite laterite, Western Australia

A deposit model for carbonatite and peralkaline intrusion-related rare earth element deposits

“…As lateritic weathering progresses, the REEs can be released from the more stable phases (Bao and Zhoa, 2008). In the lateritic zone, REEs can be present within: (1) primary igneous minerals, such as apatite, monazite, xenotime, and zircon; (2) secondary minerals that include apatite, monazite, cerianite, churchite, florencite, gorceixite, plumbogummite-group (part of the crandallite subgroup), and rhabdophane; and (3) clays and iron and aluminum oxyhydroxides (Mariano, 1989a, Lottermoser, 1990Wu and others, 1990;Morteani and Preinfalk, 1996;Bao and Zhoa, 2008). Secondary REE minerals formed in this environment are commonly fine grained and occur as polycrystalline aggregates (Mariano, 1989a).…”

“…At Mount Weld, gangue minerals include goethite and hematite with minor calcite, cryptomelane, dolomite, hollandite, kaolinite, maghemite, montmorillinite, magnetite, pyrochlore, ilmentite, and rutile, and traces of quartz, barite, anatase, and vermiculite (Lottermoser, 1990). Gangue minerals in laterites of Araxá and Catalão include gorceixite, goethite, hematite, magnetite, gibbsite, kaolinite, quartz, vermiculite, and barite (Morteani and Preinfalk, 1996).…”

“…Optimal conditions for the formation of substantial lateritic zones include a topography that allows the entrapment of newly formed residual minerals and a tectonically stable region so that denudation rates are low and the weathering profiles are preserved. Detailed descriptions of mineralogical and chemical variations in lateritic profiles at REE deposits can be found in Mariano (1989a,b), Lottermoser (1990), Wu and others (1990), Morteani and Preinfalk (1996), and Bao and Zhoa (2008).…”

“…Detailed mineralogical analyses at Mount Weld led Lottermoser (1990) to conclude that the LREEs primarily sequester into the secondary minerals rhabdophane, monazite, and the plumbogummite-group. The HREEs were mobilized further down the weathering profile and became adsorbed onto non-crystalline phases and incorporated into churchite.…”

“…In Canada, geochemical surveys of lake waters, using F, U, and Pb as pathfinders, and glacial deposits led to discoveries of REE deposits (summarized in Richardson and Birkett, 1996b). In regions with deep, intense weathering, such as laterite weathering of the upper parts of carbonatites in Brazil and Australia, the laterites contain resistate ore minerals, such as pyrochlore and monazite (Lottermoser, 1990;Morteani and Preinfalk, 1996).…”